This invention relates to fastening means for a load-bearing structure. More particularly, the invention relates to fastening means of the bolt and nut type which are employed with structural members adjacent to each other at two spaced apart points and which serve to connect the members together and to transfer load forces between the members at both points.
In load-bearing truss systems and the like, structural members frequently are connected to other structural members at spaced apart points for transfer of load forces therebetween. Examples include the use of tubular struts in the truss systems and their connection to chord means having walls or webs disposed on opposite sides of the struts. Structures of this type, which employ rectangular tubular chords as well as rectangular tubular struts, are disclosed in U.S. Pat. No. 3,826,057. Other structures similarly employ rectangular tubular struts and pairs of channel-shaped chords secured on opposite sides of the struts. In such structures, the structural members are connected together by bolts having elongated shanks with bearing diameters for supporting the structural members thereon, and clamping nuts, as illustrated in FIG. 20 of the foregoing patent, or by multiple standard bolts and nuts serving to clamp adjacent walls or webs together.
The use of standard bolts and nuts is accompanied by several disadvantages: connections for load transfer are made by tightening the fasteners, placing the fasteners under relatively high axial tension and requiring a large thread for structural integrity. More care is required for proper assembly, more fasteners are required, and more effort is involved in assembly and disassembly.
The type of fastener employed in the patent identified above obviates disadvantages of the standard fasteners but suffers from certain other disadvantages. Thus, as illustrated in FIG. 20 of the patent, load forces are transferred between the structural members at the bolt shank (129), in shear. There is the risk, however, that full bearing support on the shank will not be achieved, such as when the bolt is not inserted fully or when dimensional variations are encountered. Another disadvantage is that the bolts have to be worked through a succession of holes at spaced apart locations, which may be time-consuming with structural members out of alignment, and the close-fitting shank must be pushed entirely through the walls or webs near the bolt head. The assembly operation may be injurious to the bolt thread. As illustrated in FIG. 19 of the patent, a drift pin is employed to align the structural members and protect the thread, and it must be placed on and removed from each bolt that is inserted in the structure.